Facebook is expected to hit 1 billion users sometime this summer, possibly in August 2012. The new estimate was made by extrapolating the social network's current grown rate and using a simple process of linear regression on the data from the end of 2008.

You can thank the UK digital marketing company iCrossing for doing the hard work as seen in the graph above. It's clear by just glancing at the data that Facebook was previously growing at an exponential rate, but has recently slowed to a linear growth.

This is likely because the company's quick expansion in many of its early adopting countries (such as those in North America and Europe) has slowed: most of those countries' populations interested in social networks are already using the world's biggest one. Developing countries are now increasing interest as well, however, and are thus keeping the growth more or less steady.

Two big countries in the second category are Brazil (16 percent on Facebook) and India (just 3 percent on Facebook), both of which have a potential of millions in new members for Menlo Park. In the last nine months, iCrossing says the former jumped 13 million to 30 million users and the latter increased its number from 22 million to 36 million users.

Facebook offers two types of metrics for its user base: total number of active users (800 million) and total number of mobile active users (350 million). Both numbers are as of September 22, 2011, and haven't been updated since.

I actually think Facebook will actually hit 1 billion users before August, but I have no internal data to back that claim up. When do you think the social networking giant will see the seven digit figure?